Avian Conservation and Ecology (Jun 2020)
Nest microhabitat influences nest-site selection in dry prairie but not in pasture habitat for the endangered Florida Grasshopper Sparrow (Ammodramus savannarum floridanus)
Abstract
Vegetation characteristics can influence nest-site selection and nest survival of birds. The Florida Grasshopper Sparrow (Ammodramus savannarum floridanus) is a critically endangered ground nesting grassland bird endemic to central Florida. Currently, the two largest remaining populations are found on sites with differently managed habitats. One site is burned regularly to maintain native dry prairie habitat and the other is a cattle pasture that is mowed and burned to optimize cattle forage. Little is known about how vegetation influences Florida Grasshopper Sparrow nest-site selection and nest success in these different habitats. We measured microhabitat characteristics (percent vegetation cover and grass height) at Florida Grasshopper Sparrow nests and paired random plots at both sites for three breeding seasons (2014-2016). Percent cover differed significantly between the sites for seven of eight vegetation types, with the cattle pasture characterized primarily by grasses and dry prairie characterized by more diverse native vegetation. Despite these vegetative differences, grass height did not differ at the two locations, suggesting that plant height, rather than plant species composition, may be more important for nest site selection in this bird. Microhabitats around nests at the dry prairie site had 31% less bare ground and 32% more grass than non-nest plots. No variables predicted the placement of nests at the cattle pasture, possibly because of the more homogenous habitat at that site. We did not find a vegetative component of nest success, which suggests that other nonvegetative factors may influence nest predation. Understanding the vegetation characteristics associated with Florida Grasshopper Sparrow nests will help inform habitat management strategies for maintaining vegetation height for nest-site habitat of this critically endangered subspecies.
